When to step on that scale??

I think once a week or every few weeks is healthy. The scale can show progress, but it is not the only or even most effective representation of health. Weighing too much can cause unnecessary discouragement and, as you said, obsession because weight can fluctuate for a variety of reasons that have nothing to do with actual fat gain. Focus more on how you feel and how your clothes fit. Are you stronger or more energetic?Those are more accurate and more important!